1. Field of the Invention
This invention relates to printed circuits and methods of manufacture which permit the achievement of high density, multilayer circuits using photolithographic techniques and with a highly adaptable physical structure.
2. Description of the Prior Art
Printed circuits provide a quick, convenient and economical means of selectively interconnecting multiple circuit components which might include simple capacitors, inductors and resistors; active components ranging from simple diodes to complex integrated circuit chips; or even other printed circuits having components mounted thereon. As technology has advanced the need has arisen for printed circuits which may have more layers of more complex printed circuitry and which may have greater flexibility of physical structure while remaining economical.
One of the most common printed circuit arrangements is a phenolic resin, glass, metal or other substrate having conductive printed circuitry printed on one or both sides. However, such arrangements are limited in circuit density, require plated through holes for interconnection between sides and consume considerable surface area, thereby reducing the area available for desired conductive circuit patterns.
It is also known to form printed circuits on temporary substrates as described in U.S. Pat. Nos. 2,692,190; 2,721,822; 2,724,674; and 3,181,986. However, the arrangements do not lend themselves to the high density, fine line resolution, multilayer printed circuits of the type taught herein. A multilayer printed circuit using a permanent dielectric substrate is taught in U.S. Pat. No. 3,350,498. However, this arrangement uses 70 mil thick circuit layers compared to circuit layers varying from 0.6 mil to several mils for the present invention and is not compatible with high resolution photolithographic techniques.